36 Pathfinder tanding Sire Workshop N95- 16199 MAJA VALLES AND THE CHRYSE OUTFLOW COMPLEX allow investigations of Mawrth Valles. The region near the mouth SITES. J. W. Rice, Department of Geography, Arizona State of Mawrth Valles would be of interest because this area contains p \ University. Tempe AZ 85287, USA. material that appears to have been dissected, thus exposing the stratigraphy of what may possibly be deltaic sediments. c Mala Valles Region: This candidate landing site is located at 19"N, 53.5"W near the mouth of a major outflow channel, Maja N95-,1@00-* I Valles, and two "" channel systems, Maumee and Vedra Valles. This region has been mapped in detail by Rice and dTEVALLES SITE. J. W. Rice, Department of Geography, De Hon and is in press as a USGS 1:5oO,OOO scale geologic map. Arizona State University, Tempe AZ 85287, USA. The advantages to this site are the following: Two distinct channel forms (outflow and dendritic valley network) in one location. These This site is located at 16ON, 177OW on the flood plains of Marte channels were formed by different processes. The Valles, which is perhaps the youngest channel system on Mars. are believed to have formed by catastrophic release of water and the However, the coordinates for the landing site are flexible. Moving valley networks by surface runoff and or sapping. The ideal landing the site more to the southwest would allow investigations of pos- site, if it could be pinpointed, would be on the fan delta complex sible lacustrine sediments. The channel extends for about 3000 km located at the terminus of the three channels (Maja, Maumee, and from southeastern into western . Vedra Valles). The fan delta complex would be a fairly smooth This system appears to originate within the knobby cratered mate- surface with shallow slopes. rial around Rupes, a set of en echelon fractures that extend Water was impounded behind the wrinkle ridge system, Xanthe for more than 1000 km. Crater counts indicate that this system is Scopulus, forming a temporal lake. This paleolake bed would also in age. This channel may have also acted as a spillway present itself as a safe landing site, perhaps similar to playas. Once between paleolakes located in Elysium and Amazonis Planitia. The the wrinkle ridges were breached the water flowed northeastward young age of this channel warrants investigation because of climatic in the direction of the Viking I lander, some 350 km away. implications for fluvial activity in recent geologic time. The paucity Objectives to be analyzed in this region are (I) origin and of craters makes this an excellent site in terms of safety require- paleohydrology of outflow and valley network channels, (2) fan ments. Detailed work by Tanaka and Scott indicate that embayed delta complex composition (this deposit located in this area is one craters larger than 1 km diameter appear embayed by the channeled of the few deposits identified at the mouths of any channels on the plains unit, suggesting that it is only tens of meters thick. This planet), and (3) analysis of any paleolake sediments (carbonates, material contributed to the resurfacing of the northern lowlands of evaporites). Another advantage to this area will be any blocks and the planet. Some of the objectives stated previously for the Maja boulders that were plucked out and carried along the 1600-km Valles Region would also apply to this site (grab bag of rock types, course of Maja Valles. These samples would provide a virtual grab etc.). This site is below the 0-km datum, located at 16ON. and has bag of lithologies. For example, the oldest mappable rock unit (Nb. the young channeled plains, b